Facebook opened its new London office on Monday with the promise of a further 800 jobs in the capital next year, underlining its commitment to Britain once it leaves the European Union.

The investment, which makes London the biggest Facebook engineering hub outside the United States, was welcomed by finance minister Philip Hammond, who was given a tour of the new building located off Oxford Street in the heart of the city.

"It's a sign of confidence in our country that innovative companies like Facebook invest here," Hammond said.

Facebook announced its expansion in November last year, shortly after Google said it was building a new London hub that will accommodate more than 7,000 workers in total.

The twin announcements were seen as a vote of confidence in London's future as a technological hub despite the decision to leave the European Union which has thrown Britain's future trading relationships into doubt.

"The UK's flourishing entrepreneurial ecosystem and international reputation for engineering excellence makes it one of the best places in the world to build a tech company," EMEA vice president Nicola Mendelsohn said.

The new hires take Facebook's total staff in London to 2,300, she said, working on products ranging from virtual reality to Workplace, its enterprise platform that is being used by organizations such as Royal Bank of Scotland and Oxfam.

Tech companies have raised concerns about their ability to recruit engineers and other workers from across Europe and further afield after Britain severs ties with the EU.

Mendelsohn said the access to the best talent was Facebook's priority.

"We have made our case to government that one of the main things that we want is a stable regulatory environment in which we can operate and thrive," she said in an interview.

LONDON INCUBATOR

The new office, which has been designed by architect Frank Gehry, will also house Facebook's first in-house start-up incubator, called LDN_LAB, designed to help kick start fledgling British digital businesses by giving them access to expertise and advice from Facebook teams in the building.

"The emphasis on engineering and the 800 new jobs being created shows London remains at the forefront of global innovation," London Mayor Sadiq Khan said in a statement.

"What's more, the launch of the company's incubator is set to play a crucial role in attracting vital talent to London and will help to pave the way for the next generation of successful start-ups."

Applications for the start-up program opened on Monday, Mendelsohn said.

Facebook has faced criticism from some European and U.S. lawmakers that it is not doing enough to stop users posting extremist content or fake news stories.

Mendelsohn said Facebook took abuse of its platform very seriously, and it had recently announced a substantial investment in tackling the problem, with the number of people working on such issues set to double from 10,000 to 20,000 by the end of next year.